Cladding glass compositions for light transmitting glass fibers

ABSTRACT

Cladding glass compositions are disclosed for use in producing light transmitting glass fibers. These fibers are composed of a central core glass surrounded by an outer cladding glass. The cladding glasses have the following range of proportions (by weight): SiO2, 58-65%; Al2O3, 8-10%; CaO, 0 to 4%; MgO, 0 to 2%; B2O3, 10-12%; Na2O, 13-15%; and Li2O, 2-3%.

,XR 318 111882 m U [1! l6 ntate:

Wolf 4 1 Oct. 15 1974 [5 1 CLADDING GLASS COMPOSITIONS FOR 3.008.841l1/I96l Ticdc l06/54 LIGHT TRANSMITTING GLASS FIBERS g; 3 52 75Inventor: Warren w. Wolf, Columbus, 01110 1 m y "f [73] Assigneez owenscoming Fiberglas V FOREIGN PATENTS OR APPLICATIONS Corporation, Toledo,Ohio 214,055 5/1968 U.S.S.R l'06/52 [22] Flled: 1972 Primary Examiner-Helen M. McCarthy [21] Appl. No.: 298,128 Attorney, Agent, or FirmCarlG. Staelin; John W.

Related Us. Application Data Overman; PatrIck P. Pacella [62] Divisionof Ser. No. 113,688, Feb. 8, 1971,

abandoned. [5 7] ABSTRACT Cladding glass compositions are disclosed foruse in [52] Cl 106/50 106/54 producing light transmitting glass fibers.These fibers are composed of a central core glass surrounded byan l'outer cladding glass. The cladding glasses have the fols s q 21% 1? 18985? ll/l f o; a; 3,0t040; g0,0to2o; [56] B 0 10-12%; Na o, 13-15%; and1.1 0, 24%. 2,877,124 3/1959 Welsch 106/54 1 Claim N0 Drawings 1 3am 882e t 1 QR- {NilO/SO T? CLADDING GLASS COMPOSITIONS FOR LIGHT TRANSMITTINGGLASS FIBERS This is a division, of application Ser. No. 113,688, filedFeb. 8, 1971 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the field of fiberoptics where light is transmitted from one point to another by smalldiameter fibers. These light transmitting fibers are composed of acentral core surrounded by an outer cladding or sheath. This inventionspecifically relates to cladding glass compositions for lighttransmitting fibers made of glass.

In the fiber optics field individual light transmitting fibers orfilaments are bundled together to form light pipes. The fibers used toproduce light pipes are flexible. Therefore the light pipes can becurved around obstacles or placed in remote areas where common lightsources such as light bulbs are unsafe or hard to install.

Light pipes are useful as monitoring and lighting devices inautomobiles, aircraft, appliances, computers and medical instruments.They are particularly useful where noncurrent carrying and thereforenonshorting or nonsparking light transmitting devices are required forsafety.

Light pipes are used in some late model automobiles. They are run fromthe automobile headlights and tailights to the dashboard. As long as theheadlight or tailight is operating, the light pipe transmits light andshows the driver that the lights are on. If one of the lights fails, nolight is transmitted by the light pipe connected to that light and thedriver knows that the bulb has burned out.

Light pipes are also useful for lighting dashboard or control panelinstruments. By running many light pipes from a single, easilyaccessible light bulb to each of the panel instruments, the need formany small, remotely located light bulbs is eliminated. Only one bulb isneeded to light all instruments. And only one light bulb needsreplacing.

Light transmitting or optical fibers are usually made of either plasticor glass. Glass fibers are preferred over plastic fibers because oftheir high heat resistance. The ability of glass to withstand adversetemperature and humidity conditions for long periods of time is also afactor in selecting glass fibers over plastic fibers. While plasticfibers become brittle and discolor at temperatures above about 175F. orshow a reduction in light transmission when exposed to long periods ofhigh heat and humidity, glass light pipes are unaffected by highhumidity and temperatures in excess of 550F.

Individual optical fibers or filaments used in light pipes are composedof two essential parts, namely a central core and an outer cladding orsheath. The cladding surrounds the core. The index of refraction of thecore is higher than the index of refraction of the cladding. Due to thisdifference between the index of refraction of the core and cladding, thelight entering one end of a fiber is internally reflected along thelength of the fiber. The principle of total internal reflection explainsthis result. This principle says that a light ray traveling from amaterial with a higher refractive index (core) to a material with alower refractive index (cladding) will be reflected at the interface ofthe two materials.

ease with which the cladding glass can be laid over the core glass. Andwhen conventional glass fiber forming processes are used to make opticalfibers, compatability of the core and cladding is crucial.

Conventional glass fiber forming processes draw fine glass fibers fromsmall holes in the bottom of a reservoir of molten glass. The usualproblems of forming fibers the conventional way are multiplied whenmaking optical glass fibers. Two supplies of molten glass are needed;one of the core glass and one of the cladding glass. Then a compositefiber, -90% core and/1 10-15% cladding, is pulled from the glasssupplies. To

be able to do this at commercial speeds and form comu merciallyacceptable products the composition of the core and cladding glassesmust be carefully chosen.

SUMMARY OF THE INVENTION This invention discloses cladding glasscompositions useful in the production ora'tizi'fgfg'hfiasfrhese claddingglass compositions can be combined with compatible core glasscompositions to form optical fibers. These fibers will transmit lightand have the physical properties required in most commercialapplications. And these cladding glasses can be combined with core glasscompositions using conventional fiber forming techniques. I

The cladding or sheath glasses of this invention fall within thefollowing range of proportions:

Percent by Weight Ingredient SiO 58 65 A1 0 8 10 C210 up to 4 MgO up to2 8 0 I0 12 Na O l3 l5 Li,0 2 3 Cladding glasses in this range ofingredients have an index of refraction of about 1.50 to I52. Thesecladding glasses can be used to make light transmitting fibers bycombining them with core glasses having an index of refraction of about1.56 to L65. I

DESCRIPTION OF THE INVENTION This invention discloses cladding glasscompositions useful in the production of glass fibers which transmitlight. These compositions are useful in making optical fibers withconventional glass fiber forming techniques.

Preferred cladding glass compositions of this invention fall within thefollowing range:

Ingredient Percent by Weight SiO 64 65 A1 :4 9 B 0 11 l2 Na O 13 lI.i.,0 2 3 Core glass compositions compatible with the cladding glasscompositions of this invention may have the following range ofproportions:

Ingredient Percent by Weight 2 23 41 A1 0 7 8,0,, 2.5 1 1 K 0 up to 10B210 34 59 Sb O up to 0.05

These core glass compositions are disclosed and discussed in copendingU.S. patent application Ser. No. 827,056, filed May 22, 1969.

Specific cladding glass compositions embodying the principles of thisinvention are set forth in Examples 1 through 5.

hours Log Viscosity Temp., F.

Example 2 Ingredient Percent by Weight SiO- 61.9 A1 0 9.6 B 0 10.9 Na O15.0 Li O 2.3

No devitrification at 1455 to 1850F. over a period of 64 hours Liquidus:

Log Viscosity 2 .0

Example 3-Continued Ingredient Percent by Weight Mole Percent Example 4Ingredient Percent by Weight Mole Percent sio, 61.44 63 A1 0 8.28 5 8 0;11.29 10 Na O 14.09 14 L1 0 2.43 5 CuO 1.82 2 MgO 0.66 1

Liquidus: N0 devitrification at 1310 to 1810"F. after 16 hrs.

Log Viscosity Temp., F.

Example 5 Ingredient Percent by Weight Mole Percent Si0 58.7 60 A1 0 18.3 5 B 0 11.3 10 Na O 14.1 14 L1 0 2.4 5 C110 3.7 4 MgO 1.3 2 Liquidus:No devitrification at 1310 to 1810F. after 16 hrs Log Viscosity Temp. F.

The refractive index of each of the cladding glasses in Examples 1through 5 is between 1.50 and 1.51.

The silica (SiO content of the cladding glasses in Examples 1 through 5should not exceed about by weight of the composition. Higher amounts ofsilica can result in seed formationwhich can cause fiber breakage as thefibers are being drawn from a molten supply of glass.

A1 0 B 0 and Na O are included in the cladding glasses to controlliquidus. Li O is added as a fluxing agent.

CaO and MgO may be added (as in Examples 3, 4, 5) to increase thedurability of the cladding glass. In Examples 3, 4 and 5 these oxideswere added in place of equivalent amounts of silica to alter theviscosity and obtain a more fluid glass.

No devitrification or crystallization was noted in the glasses ofExamples 1 through 5 over a large temperature range. This means thatthese glasses have a safe, wide working range. They will offer, inproduction, a long dwell time for the cladding. This is important inmaking optial glass fibers since the cladding glass only accounts for10% of the composite fiber. Since less cladding is used it generallystays in a molten condition longer than the core glass. If the claddingglass can be kept in a vitreous or glassy (i.e., no crystals) state overa wide temperature range it will certainly aid in smooth anduninterrupted production. This is because crystals in either the core orcladding glass can cause fiber breaks and production shutdowns.

Any one of the cladding glasses of Examples 1-5 may be combined with acore glass having a composition within the above mentioned range ofacceptable core glass proportions. These combinations of core andcladding glasses would produce light transmitting glass fibers.

A preferred combination of core and cladding glasses in the claddingglass of Example 1 and a core glass having the following composition:

Ingredient Percent by Weight SiO 3 A1 0 B2021 K 0 BaO z a This coreglass is substantially the same as the core glass of Example 3 of US.patent application Ser. No. 827,056, filed May 22, 1969.

Light transmitting fibers made from this core glass and the Example 1cladding glass have a numerical aperture of 0.54 and tensile strength of210,000 psi. More than 60 percent of light entering five foot lengths ofthese fibers will be internally reflected and transmitted out theopposite end. In a fifteen foot length 28% of the entering light istransmitted. Comparable properties are believed attainable by thecombination of any of the other disclosed cladding and core glasses.

It has been found that if the overall fiber diameter of an individualoptical fiber is in the range of 1.5-2.5 mils the fiber possessesdesired flexibility and handling characteristics which help eliminatefiber breakage problems. Fibers having a diameter substantially inexcess of 2.5 mils have descreased flexibility and consequent highincidence of breakage. Conversely, fibers having a diametersubstantially less than 1.5 mils are found to be deficient intransmitting the desired amount of light;

this follows from the fact that below 1.5 mils the crosssectional lighttransmitting area is greatly reduced. Of the preferred 1.5-2.5 mil fiberdiameter, about -90% should be composed of core glass and 10-1 5%cladding glass. Although a cladding glass layer as low as 5% of thetotal fiber diameter has been placed on core glasses, the ability tocontrol such a thin layer and maintain a continuous cladding layerbecomes a major problem at commercial fiber production rates. Since anydiscontinuity of the cladding glass is detrimental to lighttransmission, it has been found advisable to keep the cladding glasslayer at about 10 percent of the overall fiber diameter.

Modifications and variations within the scope of the appended claims areintended to be included.

1 claim:

1. A light transmitting glass fiber comprising a core glass surroundedby a cladding glass;

said core glass having an index of refraction greater than said claddingglass; and said core glass consisting essentially by weight of:

sio

23-41 AI Q 7-10 B 0 2.5-11 K 0 up to 10 BaO 34-59 Sbgog up to 0.05

SiO 64-65 A1 0 8-9 B 0 1 ll 2 Na,0 1 3-1 5 M 0 2-3

1. A LIGHT TRANSMITTING GLASS FIBER COMPRISING A CORE GLASS SURROUNDEDBY A CLADDING GLASS, SAID SORE GLASS HAVING AN INDEX OF REFRACTIONGREATER THAN SAID CLADDING GLASS, AND SAID CORE GLASS CONSISTINGESSENTIALLY BY WEIGHT OF: